1. Field of the Invention
The present invention relates generally to a clutch assembly for use in conjunction with a tying mechanism on a baler and, more particularly, is concerned with improvement of such clutch assembly to enhance the functioning of the tying mechanism.
2. Description of the Prior Art
A conventional baler has a fore-and-aft extending bale case within which a plunger is reciprocably driven through working and return strokes for forming a bale of crop material in the bale case. The baler also commonly has a tying mechanism mounted above the bale case and needle means mounted below the bale case, the latter being operable to carry strands of banding material upwardly through the bale case to the tying mechanism upon completion of formation of a bale in the bale case by the plunger.
The tying mechanism conventionally includes a main transverse rotatable drive shaft and a plurality of side-by-side tying units mounted therealong. The shaft is rotated through one revolution during each tying cycle. Each rotation of the shaft causes the needle means to be moved in and out of the bale case delivering the strands to the tying units and the latter to form a tie in each of the strands received from the needle means.
The reciprocation of the plunger and each rotation of the drive shaft are precisely timed so that the needle means is projected across and then retracted from the bale case and the tying operation is completed during the internal between the last working stroke of the plunger which completed the bale to be tied and the next successive working stroke of the plunger for starting the next bale.
For rotatably driving the tying mechanism drive shaft through one revolution during each tying cycle, a clutch assembly is ordinarily utilized, being mounted on one end of the drive shaft adjacent the tying units. The clutch assembly commonly includes a first clutch part drivingly connected to the shaft and an adjacently-positioned second clutch part rotatably journalled on the shaft and carrying a chain sprocket. A drive chain drivingly connects a power driven component of the baler to the sprocket so that the latter, together with the second clutch part connected thereto, is constantly driven. The first clutch part includes a pivotally mounted pawl element which is spring-loaded to move into driving engagement with a drive lug mounted on the constantly rotating second clutch part. However, as a bale is being formed in the bale case, a stop operatively interconnected to a bale length measuring mechanism on the bale case engages an outer end of the pawl element so as to retain the pawl element against its spring bias and at a retracted position out of the path of revolution of the drive lug on the second clutch part. With the pawl element held at its retracted position, the clutch parts are disengaged and the first clutch part and the drive shaft both remain stationary.
Once the bale is completed to a predetermined length, the bale length measuring mechanism causes the stop to release from the pawl element, whereby the pawl element due to its spring bias pivots into the revolution path of the drive lug on the second clutch part. A drive connection is then formed between the first and second clutch parts by the engagement of the pawl element of the former with the drive lug on the latter. The first clutch part, and therewith the shaft, rotate with the second clutch part, but only through one complete rotation cycle. At the end of the single rotation cycle, the stop, which had automatically moved back into the path of the pawl element after the pawl element was released and moved past the stop, engages and causes the pawl element to pivot back to its retracted position which disengages the first clutch part from the second clutch part and thereby ceases rotation of the first clutch part and consequently rotation of the drive shaft.
Concurrently, with each single rotation cycle of the first clutch part and the drive shaft, a lever arm fixed to the first clutch part and another lever arm fixedly mounted to the other end of the shaft are rotated in unison therewith and through interconnecting linkages drivingly move the needle means through a complete cycle which brings the same through the bale case to deliver the strands to the tying units and then withdraws the needle means from the bale case back to its rest or home position. Also, concurrently, with each single rotation cycle of the drive shaft, components of the tying units are operated to form ties in the banding strands delivered thereto by the needle means.
Over the past years, the above-described clutch assembly as proven to be an effective means for driving the needle means and operating the tying units during each tying cycle in a precise timed relation with the reciprocation of the plunger. However, with more recent baler models, the plunger speed has been increased to ninety or more strokes per minute. Consequently, the needle means and the components of the tying units must correspondingly move and operate at higher rates.
Under such conditions, when the pawl element of the first clutch part engages the moving drive lug of the rotating second clutch part, an initial high peak starting load is exerted on the first clutch part and the drive shaft in order to initiate movement of the needle means and operation of the tying unit components. Once rotation of the first clutch part and the drive shaft begins, and therewith movement of the needle means and operation of the tying unit components, the accelerating momentum imparted thereto soon causes the first clutch part and shaft to rotate faster than the second clutch part, whereby the pawl element of the first clutch part overruns or advances out of engagement with the drive lug on the second clutch part. However, the drive lug on the second clutch part soon catches up with the pawl element of the first clutch part after the initial starting momentum imparted to the needle means and tying unit components has dissipated. When the drive lug catches up to the pawl element and engages the same again, a second peak load condition is exerted by the second clutch part on the first clutch part and drive shaft before the end of the tying cycle is reached. These successive peak loading and overrun conditions are reflected by a momentary hesitation in the movement of the needle means and in the operation of the tying units during each tying cycle. Such conditions cause increased wear on the drive shaft and components of the tying units operatively associated therewith and ultimately may result in tying malfunctions.